The ability of cells to process a large number of extracellular signals into the appropriate array of intracellular responses depends on the types of signaling pathways that are expressed in the plasma membranes. The most common type of signaling pathway relies on the interaction of three proteins: receptors, G proteins, and effectors. The receptors are responsible for recognizing and discriminating between a multitude of extracellular signals. The G proteins are responsible for transmitting signals from one or more receptors to the appropriate effectors. The effectors are enzymes and ion channels, which are responsible for modulating the concentrations of intracellular signals, including cAMP, IP3, diacylglycerol, and various ions. The recent identification of more than 100 different receptors, more than 320 possible combinations of G protein heterotrimers, and an unknown number of effectors raises important questions as to how these signaling pathways are assembled to ensure the correct transmission of a signal from a particular receptor to a specific effector. Given its interposition between receptor and effector, much of the fidelity of signal transmission must reside in the subunit structure of the G protein. Each G protein has a characteristic alpha, beta, gamma subunit structure. Because the alpha subunit has been thought to specify the function of a particular G protein in receptor-effector coupling, most research has focused on this subunit. As a result of this research, the existence of 16 different alpha subunits has been revealed by molecular cloning. While it has generally been assumed that structural heterogeneity of the alpha subunits provides the specificity for receptor-G protein and G protein-effector interactions, a growing body of evidence indicates that similar structural heterogeneity of the beta and gamma subunits exists, and that this heterogeneity contributes to the specificities of these interactions. The primary goal of this research proposal is to define the contribution of the beta, gamma subunits of the G proteins in ensuring the correct transmission of a signal from a particular receptor to a specific effector. To achieve this goal, we will: 1) examine further the structural diversity of beta and gamma; 2) determine the selectivity of beta and gamma interactions; 3) examine the selectivity of alpha and beta, gamma interactions; 4) address the role of beta, gamma in contributing to the selectivity of receptor interaction, using in vitro strategies; 5) confirm the role of beta, gamma in contributing to the selectivity of receptor interaction, using in vivo approaches; and 6) begin to analyze the structure-function relationships of gamma.